1. Technical Field of the Invention
The present invention relates to a mobile telecommunications system and, in particular, to the dialing of a B-number for originating a call within a Public Land Mobile Network.
2. Description of Related Art
In a conventional mobile telecommunications network, such as an analog cellular telecommunications network, whenever a mobile subscriber enters a local directory number, the mobile station automatically retrieves a Numbering Plan Area (NPA, more commonly known as an area code) number assigned to the mobile station and prepends it to the dialed local directory number. This is because the serving mobile telecommunications network needs a complete B-number including both the NPA number and the seven digit local directory number to properly process the call setup request. Accordingly, whenever the mobile subscriber dials only a seven digit local directory number (such as 555-1212), the mobile station presumes that the mobile subscriber wishes to dial another local number within the same NPA area and prepends the mobile station's own NPA number to the dialed local directory number. For example, if the mobile station has been assigned a 214 NPA number, the above dialed 555-1212 will be transformed to 214-555-1212 before being transmitted to the serving mobile switching center (MSC).
With the introduction of the Personal Communications System (PCS), mobile stations no longer transmit NPA numbers to the serving MSC when requesting an outgoing call setup. Furthermore, because there are usually more than one NPA value per particular geographic area, it is no longer consistent to presume that the NPA number for a dialed local directory number is the same NPA number assigned to the requesting mobile station.
As an illustration, the Dallas, Texas area is served by two different NPA numbers. The 214 NPA number serves the majority of the Dallas area. The newer 760 NPA number has been assigned to serve some suburban areas outside of the Dallas city limit, but still within the Dallas county jurisdiction. If a mobile subscriber subscribes to a mobile service and is assigned the 760 NPA number for his mobile station, yet uses his mobile service mostly within the 214 area, the mobile subscriber has to enter the 214 NPA number for each of his outgoing calls. Furthermore, if the mobile subscriber travels into a visited PLMN (roaming) area and tries to use his telecommunications service to originate local calls, the mobile subscriber again has to enter the corresponding NPA number for that particular PLMN. This is because the visited PLMN does not know which NPA number to utilize when a roaming subscriber dials only a local directory number.
Therefore, it would be advantageous to remove the logical relationship between the NPA number to be assigned to dialed local directory numbers and the NPA number assigned to the mobile station. It would further be advantageous to enable a mobile subscriber to selectively designate a particular NPA number to be used with all subsequently dialed local directory numbers.